Connecting Delta Cities (CDC) was set up to share best practice in adapting to climate change and consequent sea level rises for delta cities. They are holding their first conference at the end of this month.

With more than 50% of the world's population now living in urban areas and more than two thirds of the world's cities vulnerable to rising sea levels, water management and flood defense forms an important part of climate adaptation. (See the diagram, When Sea Levels Attack! from Information is Beautiful for a sense of the scale of the problem of rising sea levels and the vulnerability of many major cities.)

The CDC network grew out of the C40 organization, which is a group of large cities dedicated to fighting climate change. Eight cities currently form the core of the CDC network: Tokyo, Jakarta, Ho Chi Minh City, Hong Kong, London, Rotterdam, New York and New Orleans. Some of these cities are more vulnerable than others: the closer the lower parts of the city lie to sea level and the poorer the country in which the city is situated, the greater the vulnerability.

This film surveys three of the cities that have joined the Delta Cities Network -- New York, Jakarta and Rotterdam -- and describes how rising sea levels are already affecting them and how they are beginning to respond. New York's subway is vulnerable to flooding, something which isn't helped by having the entrances at street level instead of raising them higher, although this is the level at which they are most easily used by pedestrians. Measures to reduce the subway's flooding risk are important and seem manageable. The problems described in the section on Jakarta, in part two of the film, are astounding and there are far fewer straightforward solutions. (Part one of the film is embedded below)

Parts of Jakarta are subsiding by up to 25cm per year, so that large parts of the city are flooded at high tide. The rivers and canals that flow through the city can't deal with high levels of rainfall and in fact, their maximum capacity has been reduced to 30% because of the large amounts of rubbish littering the channels. A staggering 70% of the city is now liable to be flooded after a heavy rain storm because of the inability of the city's watercourses to carry this water away quickly enough. The canals are now being dredged to improve water flow. What is really worrying however, is that while New York is considering how to face future challenges, for Jakarta these problems are very much of the present. Widespread flooding is a problem in Jakarta now, with sea levels having risen only a small amount so far.

The CDC has already started to develop a body of research in response to some of these problems, such as this piece [PDF] on developing resilient waterfronts in New York, or this one [PDF], which looks at the amount of water and sediment that rivers and canals in Jakarta are able to carry and how this is influenced by land use. Further research will be presented at the CDC's conference itself, with the results to be published at the end of October.

Alison Killing is an architect and urbanist based in Rotterdam, the Netherlands.